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Abstract：There were many radial cracks on the stainless steel flange surface after storing for five years in Nibo. Marco and micro observation, chemical composition analysis and metallurgical examination were carried out to find out the failure cause. The results show that the fracture mode is stress corrosion. The material of the flange is 1Cr17Ni7, but the not required material: 304. The corrosion resistance of 1Cr17Ni7 is poorer than that of 304. In addition, the carbide network along the grain boundaries in the 1Cr17Ni7 promoted the occurrence of stress corrosion. Key words： flange   stainless steel   stress corrosion   carbide network Introduction Flanges are generally used for parts transfer to facilitate disassembly and assembly. Flange pairs are fastened together by bolts. Pipe flange materials generally use Q235, equipment flange materials generally use 20 steel, 16Mn, 304, 316, 316L. In order to investigate the impact of the storage environment on the engine, the engine was stored in a relatively harsh and high temperature and humid South Coast. After 5 years, the inspection found that there was a serious corrosion phenomenon in the exit flanges of the 20 equipment, of which 14 equipment outlet flanges were cracking at the same time. The material used for the cracked flange is 304 stainless steel. Because of its excellent mechanical properties and corrosion resistance, the stainless steel is widely used in various corrosive environments, especially in the harsh marine environment, but the corrosion of stainless steel components and parts for a long time in this corrosive environment is not possible. In addition to the common influence of stress and corrosion, the stainless steel material will have serious stress corrosion cracking in addition to uniform corrosion, which has great destructiveness. The two major factors affecting the stress corrosion of stainless steel are internal and external factors: internal factors mainly include material composition and tissue state, and the external factors mainly include the use environment (corrosion medium concentration, temperature) and the stress state of their own. Through analyzing the causes of flange cracking, we find out the main causes of stress corrosion, and provide technical support for product storage and life extension at sea. 1 Test process and analysis Observation of 1.1 cracks and observation of crack section The macroscopic morphology of the cracked flange is shown in Figure 1. There is a serious corrosion phenomenon on the surface of the flange. 8 radial cracks are visible on the visual surface, and the cracks are not penetrable to the wall thickness. The 8 cracks are evenly distributed in the circumference, and each crack is composed of multiple intermittent cracks. After cleaning the section, the morphology observation and energy spectrum analysis are carried out under scanning electron microscope. The whole crack section is along the crystal morphology, the two cracks are visible along the crystal, and a layer of corrosion product is attached to the crystal surface. The energy spectrum analysis of the corrosion products mainly contains O, Fe, Cr and the S and Cl elements with high content; the artificial cross section is dimple. Morphology, energy spectrum analysis mainly contains Fe, Cr (19%), Ni (7.1%), Si (1%), Mn (1.9%) elements (all mass fraction). The fracture micromorphology is shown in Figure 3. The fracture characteristics above show that the cracking property of the flange is brittle fracture. Figure 3 fracture micromorphology 1.2 metallographic analysis and microhardness test After sampling and preparing the metallographic specimens near the parallel cracks, there are many basic radial cracks on the specimen (Fig. 4). 1.3 chemical composition analysis The sample and chemical method are tested on the flange, and the results show that the grade of the material used in the flange does not conform to the requirements of 304 stainless steel (equivalent to the domestic brand 0Cr18Ni9), which is in accordance with the 1Cr17Ni7, and the test results are detailed in Table 1. 2 Analysis and discussion After the export flange is installed on the equipment, it has been parking in Ningbo for 5 years. It is found that there are cracking phenomena in 14 outlet flanges of 20 sets of equipment export flanges. It is found that there is a serious corrosion phenomenon on the surface of one of the flanges, and 8 obvious radial cracks are visible, and each crack is composed of a number of intermittent small cracks. The fracture fracture observation shows that the crack section is uneven, the cross section adheres to the reddish brown corrosion product, the microstructure is along the crystal morphology, and a layer of matrix corrosion product is attached to the crystal surface, and the corrosion products contain high corrosive medium S and Cl elements. The fracture characteristics above show that the cracking property of the flange is brittle crack, and the cracking mechanism is stress corrosion. The results of chemical analysis show that the material used for flanges is 1Cr17Ni7, which does not meet the requirements of design brand 304 (0Cr18Ni9). Compared with 304, 1Cr17Ni7 is high in C content and low in Cr and Ni content, resulting in low corrosion resistance (uniform corrosion and intergranular corrosion). The results of metallographic analysis show that the cracks are all intergranular, the grain size is uneven, and there are intergranular carbide grains. The precipitation of a large number of carbide leads to the decrease of [1 – 3] in the grain boundary Cr content. The electrode potential of poor Cr region is lower than that in the crystal. Under the action of corrosion medium, the grain boundary of low electrode potential becomes anodic and is corroded, resulting in the decrease of the intergranular corrosion resistance of the material [4 – 8]. The comprehensive analysis shows that the cracking mode of the flange is stress corrosion, and the cause of stress corrosion is related to the following two factors: 1) the material used in the flange does not meet the design requirements, and the 1Cr17Ni7 material is used instead of 304 stainless steel, while the corrosion resistance and intergranular corrosion properties of the 1Cr17Ni7 material are all worse than that of the 304 stainless steel; 2) 1Cr17Ni7 matrix group Weave the intergranular carbide in the intergranular distribution, resulting in the decrease of grain boundary corrosion resistance of the material. 3 Conclusion The cracking mode of the flange is stress corrosion. The cause of stress corrosion in the flange is that the flange used 1Cr17Ni7 instead of the design requirements of 304 stainless steel, and the 1Cr17Ni7 matrix has a reticulate carbide along the crystal, which leads to the decrease of the corrosion resistance of the material. Author: Wang Ying, Xie Guojun, Han Lu, Pang Jincheng wilsonpipeline.com is a professional stainless steel flange manufacturer, producing stainless steel flanges of super double phase stainless steel, double phase stainless steel, alloy steel, stainless steel and so on. Source: China Stainless Steel Flange Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com) Reference [1] Arutunow A, Darowicki K, Zielinski A. Atomic force mi-croscopy based approach. 2011, 56 (5). [2] Dai Yongxiang, Lian Fang, Li Ji, et al. Study on intergranular corrosion behavior of 304 stainless steel [J]. light automobile technology, 2011 (5/6): 34-37. [3] Bi Hong Yun. Grain boundary engineering inhibits chromium depleted grain boundary of SUS304 stainless steel [J]. steel, 2005, 40 (6): 68-71. [4] Ye Chen Qing, Hu Rong Gang, Hou Ruiqing, et al. Scanning micro electrode method for sensitizing treatment of localized corrosion behavior of 304 stainless steel. [J]. electrochemistry, 2013, 19 (6): 507-510. [5] Jin Guangxi, Pu Meishan. Failure analysis of stress corrosion cracking of 304 stainless steel heads [J]. hot working technology, 2011, 40 (23): 226-228. [6] Hu Xiaohui 1Cr18Ni9 stainless steel clamping strip fracture analysis, [J]. failure analysis and prevention, 2008, 3 (3): 55-58. [7] Zhang Xinming, Feng Jijun, Lu Liulin, et al. Cracking failure analysis of stainless steel welded joint of thermoregulant [J]. failure analysis and prevention, 2014, 9 (6): 368-374. [8] Jiang Tao, Yu Yang, Yang Sheng, et al. Discussion on stress corrosion problems of stainless steel from failure cases. [J]. corrosion and protection, 2011, 32 (4): 297-300. [9] Wang Ying, Xie Guojun, Han Lu, Jin Cheng. Analysis of flange cracking cause [J]. failure analysis and prevention, 2016, 11 (6): 369-371.

The cleanliness of stainless steel pipe refers to the degree of contamination of the steel pipe by impurities. It is expressed by the quality, size and quantity of the impurity particles collected from the specified characteristic parts by a prescribed method. The “prescribed part” refers to the characteristic part that jeopardizes the reliability of the product. “Impurities” include all impurities remaining in the product design, manufacturing, transportation, use and maintenance, which are inherently mixed with the outside world and generated by the system. With the advancement of science and technology, the field of mechanical manufacturing is moving towards precision development, and the cleanliness of TP304 stainless steel pipes are becoming more and more important in the fields of aviation, aerospace, automobile and electronics. The residual pollutants on the surface of TP304 stainless steel pipes have a huge impact on the key performance of precision products such as precision, reliability and life. The rinsing liquid in the rinsing process during the cleaning process of the stainless steel tube is used to characterize the cleanliness of the stainless steel tube, and the cleanliness of the rinsing liquid is correlated with the cleanliness of the stainless steel tube, so that the cleaning liquid is passed through the particle size detector during the cleaning process of the stainless steel tube. Instant inspection reveals the real-time cleanliness of the stainless steel tube during the cleaning process. This correspondence is of great importance in the actual production of stainless steel tube cleaning. The stainless steel tube is cleaned according to ultrasonic cleaning, high-pressure water jet cleaning, and rinsing process. After the cleaning, the rinsing liquid is sampled in the stainless steel tube rinsing unit to check the cleanliness of the rinsing liquid. Limiting the time required for stainless steel tubes to clean high-pressure water jets for cleaning and rinsing, you can get rinses with different cleanliness. More precise inspection of stainless steel pipes corresponding to different cleansing rinses, detecting the cleanliness of the stainless steel pipe surface, and correlating the cleanliness of the rinse liquid with the cleanliness of the stainless steel pipe surface, so that the rinse can be detected immediately during the production process. The cleanliness of the liquid indirectly indicates the cleanliness of the stainless steel tube surface. The correspondence between the cleanliness of the rinse liquid and the cleanliness of the stainless steel tube surface can be obtained by simulation experiments. The aerospace industry has higher requirements for the reliability of hydraulic systems. In the United States and other Western countries, the research on hydraulic system pollution control was carried out in the aerospace field in the 1960s, and a series of system cleaning and detection technologies were born. The application of these technologies significantly improves the performance of the hydraulic system. China’s hydraulic oil and lubricant manufacturers still control the particle size of oil with less than 0.005% (mass fraction) of “mechanical impurities”, while the United States and many international organizations such as NASA and International Standards Organization (ISO) uses oil particle size and its quantity distribution to measure the cleanliness of the oil, and has developed their own pollution level standards NAS1638 and ISO 4406-1999. The particle contaminants in the liquid are pided into particle sizes, and the degree of contamination of the liquid is defined by the number of particles in each size interval. In the aviation field of China, with the improvement of the cleanliness requirements of TP304 stainless steel pipe, the research on pollution control of aircraft hydraulic system began in the 1970s, and the pollution level standard of particle counting method was also introduced, GJB420-1987, GJB420A. -96 pollution degree standard and the latest GJB420B-06 pollution degree standard, applicable to hydraulic system oil pollution test and fuel, oil and even other working fluids, providing a standard basis for China’s cleanliness field. Source: China Stainless Steel Pipe Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

Stainless steel flanges are widely used in ship pipeline engineering because of their good corrosion resistance. As an important part of pipeline connection, they have the advantages of convenient connection, easy to maintain pipeline sealing performance, and easy inspection and replacement of certain pipelines. A certain type of ship has recently purchased a batch of 304 flange. The flange is sent to the pickling plant for pickling and passivation treatment before use. The pickling tank is placed in the pickling tank for ten minutes. Corrosion was observed after cleaning. In order to find out the cause of corrosion of the batch of flanges, prevent product quality problems from happening again, and reduce economic losses, we conducted chemical analysis and metallographic examination of the batch flange samples. 1 Physical and chemical testing 1.1 Chemical composition analysis Chemical analysis samples were taken on the corrosion flange, and the chemical composition was determined by a Baird DV-6 type spark direct reading spectrometer. The results are shown in Table 1. According to the technical requirements of 304 stainless steel chemical composition in ASTM 276-2013 “Standard Specification for Stainless Steel Bars and Shapes”, the content of Cr in the chemical composition of the failed flange is lower than the standard value. Table I 1.2 Metallographic examination A longitudinal section sample was taken at the corrosion of the failed flange. After polishing, it was not etched. Under the ZEISS metallographic microscope, the non-metallic inclusions were measured according to GB/T 10561-2005. Rating chart microscopic test method: 1.5 grades of sulfides; grade 0 of alumina; grade 0 of silicates; grades of grades of spherical oxides. The sample was etched by aqueous solution of ferric chloride hydrochloride and observed under a 100 x metallographic microscope. The austenite grains in the material were found to be extremely uneven. The grain size grade was determined according to GB/T6394-2002 “Metal average grain size”. According to the method, the coarse-grained zone can be rated as 1.5 (see Figure 3); the fine-grained zone can be rated as 4.0. Figure 3 Observing the microstructure of the near-surface corrosion, it can be found that the corrosion starts from the metal surface and concentrates on the austenite grain boundary and extends into the interior of the material. The grain boundary of this region is destroyed by corrosion and the intergranular bond Almost completely lost strength, corroded. Severe metals even form powders that are easily scraped off the surface of the material. The high-magnification structure of the corrosion flange was observed by a 500x metallographic microscope, and the microstructure was austenite + a small amount of ferrite + the first phase particles precipitated on the grain boundary. 2 Comprehensive analysis The results of physical and chemical tests show that the content of Cr in the chemical composition of the stainless steel flange is slightly lower than the standard value. The Cr element is the most important element determining the corrosion resistance of stainless steel. It can react with oxygen to produce oxides of Cr and form blunt. The layer acts to prevent corrosion. Moreover, the non-metallic sulfide content in the material is high, and the aggregation of the sulfide in the local region causes the concentration of the Cr element in the surrounding area to decrease, forming a Cr-depleted region, thereby affecting the corrosion resistance of the stainless steel. Observing the grain of the stainless steel flange, it can be found that the grain size is extremely uneven, and the mixed crystal grains with uneven size in the structure easily form the difference of the electrode potential, resulting in micro-battery, which leads to electrochemical corrosion on the surface of the material. The coarse-grained mixed grain of the stainless steel flange is mainly related to the hot working deformation process due to the sharp deformation of the grain during forging. Analysis of the microstructure of the near-surface corrosion of the flange shows that the corrosion starts from the surface of the flange and extends along the austenite grain boundary. The high-magnification microstructure of the material shows the austenite on the grain boundary. There are many first phase precipitates, and the third phase accumulated on the grain boundary is easy to cause the grain boundary to be depleted in chromium, causing intergranular corrosion tendency and greatly reducing its corrosion resistance. The third phase in stainless steel mainly has fine carbides (M 23C6 ), σ phase and δ ferrite, all of which have a great influence on the corrosion resistance of stainless steel. The formation temperature of the precipitated phase of M23C6 is 450 °C-850 °C, mainly composed of metal chromium. Most of the carbides are distributed on the grain boundaries of the crystals, and some are distributed inside the crystals and crystal defects because the carbides are rich. Chromium, easily lead to chromium deficiency in the region; σ phase formation temperature is 500 ° C -925 ° C, in this temperature zone, ferrite partially or completely decomposes σ phase, 6 phase chromium content is 42% -50% It is a brittle phase with high hardness, which can cause the toughness and corrosion performance of the material to decrease. δ ferrite is a kind of high-temperature ferrite which is formed by cooling from liquid iron to 1538 °C. The phase is brittle and processed. It is easy to cause cracks and is prone to pitting corrosion. 3 Conclusion Through a series of failure analysis of corroded stainless steel flanges, the following conclusions can be drawn: (1) Corrosion of stainless steel flanges is the result of a combination of factors, in which the first phase precipitated on the grain boundaries of the material is the main cause of flange failure. It is recommended that the heating temperature be strictly controlled during the hot working process, not exceeding the upper limit temperature of the material heating process specification, and cooling rapidly after solid solution to avoid staying in the temperature range of 450 ° C – 925 ° C for a long time to prevent the precipitation of the third phase particles. (2) The mixed grains in the material tend to cause electrochemical corrosion on the surface of the material, and the forging ratio should be strictly controlled in the forging process. (3) The low content of Cr in the material and the high content of sulfide directly affect the corrosion resistance of the flange. When selecting materials, attention should be paid to the selection of materials with pure metallurgical quality. Source: China Stainless Steel Flange Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

The stainless steel pipes for condensers and heat exchangers are basically welded pipes. The investigation found that there are many cases of pitting corrosion in stainless steel pipes in the weld and its heat affected zone. At least 5 samples were investigated: 1) 125MW of a power plant in Zhejiang Unit TP304 stainless steel tube condenser. 2) TP304 stainless steel tube condenser in a power plant in Henan. 3) TP304 stainless steel tube heat exchanger in a unit refrigeration unit in Changsha. 4) 436L ferritic stainless steel tube heat exchanger in a chemical enterprise in Shandong Device. 5) Shanxi TY first thermal power plant TP304 stainless steel tube heat network heater. Failure analysis of corrosion of TP304 stainless steel pipe of TY first thermal power plant heat network heater:     (1) Overview The first stainless steel tube heater of TY First Thermal Power Plant started to run. Only one heating period was found to have micro-leakage. At the beginning of the next heating period, the first heater was stopped and a second new stainless steel tube heater was opened. Heating ended. The heater was shut down and no leaks were found before the shutdown. After more than one month of heating, the hydraulic test was conducted to check for leaks. It was found that the first stainless steel tube heater had nearly two leaking tubes, and the second heater also had hundreds of stainless steel tubes leaking. A stainless steel tube corroded by the heater was sampled and found to be etched or perforated in the vicinity of the weld. (2) Appearance The leaked TP304 stainless steel pipe has only a few pits in the weld and nearby, some have been perforated, and there are basically no pitting pits in other places, indicating that the corrosion resistance of the weld and heat affected zone is significantly lower than that of the base metal, and the manufacturing quality is problematic. . (3) Detection of chemical composition and mechanical properties According to the analysis of the test results of a large number of stainless steel materials, the possibility of unqualified chemical composition and mechanical properties of stainless steel is extremely small. Due to the improvement of modern smelting technology, the stainless steel composition can be precisely controlled, the cost of removing impurities is low, and the cost of beneficial alloying elements is high. Therefore, the content of impurities in stainless steel is usually much lower than the specified value, and the contents of the beneficial alloying elements such as nickel, chromium and molybdenum are basically at the lower limit. (4) Metallographic analysis The transverse section of the TP304 stainless steel tube was taken, and the metallographic structure of the weld was observed under an optical microscope after being inlaid, ground and polished, and chemically etched. The microstructure of the weld of TP304 stainless steel pipe is austenite with a small amount of ferrite, and it is as-cast columnar and dendritic crystal. Since the harmful elements are easily segregated between the dendrites and the columnar crystals, the corrosion resistance at the weld is poor, which is a weak link of the stainless steel welded pipe. (5) Weld corrosion ratio test In order to quantitatively characterize the difference between the corrosion resistance of the austenitic stainless steel pipe weld and the base metal, the American Society for Testing and Materials Standard ASTM A249112 specifies the test method and the qualification criteria. The austenitic stainless steel welded pipe is cut into sections, half of which are welded, and half of which is a weld-free base metal. The thickness of the weld and the base metal is measured, and then placed in boiling 20% hydrochloric acid. When the base metal is thinned to the original When the thickness is 40-60%, the sample is taken out, and the thickness of the weld and the base metal is measured after cleaning. The corrosion reduction of the weld and the base metal is calculated, and the ratio of the corrosion reduction of the weld to the base metal is called Weld corrosion ratio R. If R is equal to 1, it indicates that the corrosion resistance of the weld and the base metal are equal; if R is greater than 1, the corrosion resistance of the weld is worse than that of the base metal. ASTM A249 stipulates that R<_1.25 is acceptable, and the R value can also be agreed upon by both parties. Take the unused spare tube and test the weld corrosion ratio according to S7 of ASTM A249. The test results are shown in Table 2 5. The weld corrosion ratio R of the TP304 stainless steel pipe is about 1.52, which is much larger than 1.25, and the weld quality is unqualified. Since this quality clause is a supplemental technical provision, ASTM A249 stipulates that when the standard is implemented, it is only implemented by the acquirer when specified in the contract or order. However, general power plant technicians are not familiar with the standard, and the terms are rarely written when ordering, which is prone to quality disputes.   (6) Corrosion mechanism and prevention and control method     Stainless steel welded pipes for condensers and heat exchangers are prone to pitting corrosion in welds and their heat-affected zones. The main reason is that untreated welds are as-cast columnar and dendritic crystals, and harmful elements are easily in dendritic and columnar Segregation between crystals, if the weld is in a disadvantageous position at the bottom, or in a special environment such as pickling, the weld and its heat affected zone are more susceptible to preferential corrosion. If the uniformity of the welded pipe material is to be improved, the microstructure and performance difference between the weld zone and the base metal are reduced or eliminated, the weld or the entire welded pipe needs to be cold worked and heat treated, and the weld can be made by rolling and recrystallization. The columnar and dendritic crystals are transformed into equiaxed crystals. 1721. The flattening after heat treatment in the weld can improve the microstructure and properties of the weld, but the internal weld should have sufficient height to ensure a certain amount of rolling; heat treatment Have enough time to stay. Source: China Stainless Steel Pipe Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

1.1 chemical composition and metallographic structure The main chemical compositions of some main high alloy austenitic stainless steels are given in Table 1. Among them, Al – 6 x and 254 SMO are typical The 6 mo super austenitic stainless steel, while the 654 SMO is a typical 7 mo super austenitic stainless steel. The basic metallographic structure of super austenitic stainless steel is a typical one hundred percent austenite. But because of the high content of chromium and molybdenum, There are likely to be some metal mesophase, such as Chi and sigma. These metal mesophase often appear in the center of the plate. However, if the heat treatment is correct, the formation of these mesophase can be avoided and nearly one hundred percent austenite can be obtained. 254 SMO The metallographic organization does not have any other metal mesophase. The structure was obtained after heat treatment at temperatures of 1150 ~ 1200C. If there is a small amount of metal mesophase, they will not have corrosion resistance to mechanical properties and surfaces. It has a great influence. But try to avoid temperatures ranging from 600 to 1000C, especially during welding and hot working. 1.2 mechanical properties The austenitic structure generally has moderate strength and high Forgability. After adding a certain amount of nitrogen, the corrosion resistance is improved. In addition, while maintaining austenitic stainless steel forgings and toughness, high nitrogen super austenitic stainless steel also has very high mechanical strength. his The yield strength is 50 to 100% higher than that of ordinary austenitic stainless steel. The effects of nitrogen on mechanical properties were observed at room temperature and higher temperature respectively. Table 2 and table 3 are shown. Mechanical properties of high alloy austenitic stainless steel at temperatures of 2 + 20 1.3 physical properties The physical properties mainly depend on the austenite structure and partly depend on the chemical composition of the material. That is to say the super austenite is not Stainless steel is much different from ordinary austenitic stainless steel, such as 304 or 316, in terms of physical properties. Table 4 lists the different combinations Some of the typical physical properties of gold. Table 4 physical properties of some stainless steels and a nickel based alloy 3.1 uniform corrosion The most important alloy elements to improve the stability of stainless steel are chromium and molybdenum. The content of these components in super austenitic stainless steel is higher. Therefore, it has good corrosion resistance in various solutions. In some environments, the addition of elements such as silicon, copper and tungsten can be further improved. The corrosion resistance of the material. Figure 1 shows the equal corrosion velocity diagram of some austenitic stainless steels in pure sulfuric acid. As you can see, Stainless steels with high alloy content, such as 904L, 254 SMO and 654 SMO, are larger than normal Ordovician in larger concentration and temperature range. Stainless steel, such as 304 and 316, has better corrosion resistance. The diagram also shows that the high silicon stainless steel SX is very strong. The ability to resist concentrated sulfuric acid. Fig. 1 the equal corrosion velocity curve of some austenitic stainless steel in pure sulfuric acid, the corrosion rate is 0.1 mm / year. 2.2 Pitting corrosion and crevice corrosion Pitting corrosion and crevice corrosion are two closely related types of corrosion, all of which are localized. Its main production conditions are chlorine-containing Sub-environment. However, temperature and pH (pH) also play an important role. When the stainless steel is in a chlorine-containing environment, it must be Pitting corrosion occurs at temperature. It is well known that an increase in the chromium and molybdenum content helps to enhance the resistance of the stainless steel to localized corrosion. chromium, The combined effects of molybdenum and nitrogen on resistance to localized corrosion are often expressed in the empirical formula WS (Wirksumme). WS (PRE) = % chromium + 3.3 × % molybdenum + 16 × % nitrogen The WS value in the formula is generally referred to as the Pitting Resistance Index (PRE). Therefore, it is often expressed by PRE. Given by the formula The nitrogen factor of 16 is the most frequently used. However, other factors have been used in the literature, such as the Mannesmann Institute. Dr. Herbsleb suggested using 30. Other components such as tungsten also have a positive effect on corrosion resistance. Weight percent algorithm Calculated, the effect is about half of molybdenum. For comparison, use 16 and 30 as the coefficients of nitrogen in the PRE formula as shown in Table 1. Some steel grades calculate the PRE value. The results are given in Table 7. Table 7 PRE value and critical pitting temperature and critical crevice corrosion temperature of some high alloy stainless steel 2.3 Stress corrosion cracking Ordinary austenitic stainless steel is more susceptible to stress corrosion cracking caused by chloride than ferritic stainless steel and duplex stainless steel. However, super austenitic stainless steels have a very high resistance to stress corrosion cracking, and in many cases are superior to the ability of duplex stainless steels to resist stress corrosion cracking. Table 9 shows the critical stresses that cause stress corrosion cracking in the case of evaporation (determined by the drip test). The test time is 500 hours. It can be clearly seen that super austenitic stainless steel has excellent resistance to stress corrosion cracking compared to ordinary stainless steel. Table 9 Critical stresses leading to cracks 2.4 Corrosion in seawater The most common environment that causes pitting, crevice corrosion and stress corrosion cracking in stainless steel is in water, especially in seawater. Because the chloride ion content of sea water is very high. Since the critical point corrosion temperature and critical crevice corrosion temperature of super austenitic stainless steel are very high, see Table 7, which shows that its ability to resist local corrosion in seawater is also very strong. Therefore, super austenitic stainless steel containing 6% molybdenum and 7% molybdenum has been widely used in seawater like nickel-based alloys. As the actual situation is very different, the reported results are also very different. Some have been in good condition for a few years, and some have had serious corrosion problems within a year. As with all stainless steels in contact with chloride-containing water, the decisive factor is the oxides and tiny gaps created by welding, and the residual chlorine content is also a very important factor. Chlorine added to seawater to kill marine microorganisms is a strong oxidant that can easily cause the corrosion potential of stainless steel to exceed its critical pitting and crevice corrosion potentials. At less than 50 ° C, there should be no pitting problems on the surface of a clean 6 molybdenum super austenitic stainless steel. However, in some practical applications, there are also examples of 6 molybdenum super austenitic stainless steels having better performance at higher operating temperatures. The most restrictive factor is crevice corrosion. If the gap is severe, corrosion will occur even at temperatures of 20 to 30 ° C). However, this type of stainless steel is generally acceptable, at least at temperatures up to 30 ° C and residual chlorine content of about 0.5 parts per million. When the gap is very serious (as is the case with some types of plate heat exchangers), even if the temperature is kept below 25 °C, 6 molybdenum super austenitic stainless steel is generally not used for this type. use. In applications where the gap is severe but no chlorine is added, the use of 6 molybdenum super austenitic stainless steel has been very successful at least at a temperature of 35 °C. Source: China Super Duplex Stainless Steel Fittings Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

When welding stainless steel pipes, the requirements for the welding process are very high, because when welding them, many problems need to be solved, such as heat treatment, cold shrinkage and thermal expansion, and also attention should be paid to on-site construction. Let’s talk about their solutions in detail. The first is the construction capability. Welding is a kind of professional work. It can’t be disassembled after welding. It is very inconvenient because it needs to be changed in the actual construction site. Because argon arc welding requires special equipment, and the thickness of stainless steel pipe is very thin, there must be a certain level of welders to operate, but the actual site construction site personnel mobility is large, if the welding personnel do not have welding operation certificate, it will not Will reasonably adjust the current, argon, etc., and affected by the construction site space and human factors, often will lead to the phenomenon of virtual welding, leakage welding or even welding through the pipe, although there will be no leakage problems during the pressure test, but will There are a lot of construction hazards. After using for a certain period of time, due to factors such as thermal expansion and contraction, it will lead to water leakage in the future. The second is the heat treatment problem. As a stainless steel pipe and socket pipe fittings, it can be solution treated at the factory. However, at the construction site, the pipes and fittings are limited by the construction site and are unlikely to be solidified. In the solution treatment, since the austenitic stainless steel slowly passes through 450 to 800 degrees, carbon is precipitated, and the formed chromium carbide precipitates at the boundary of the crystal, and the chromium content in the vicinity thereof is reduced, resulting in a chromium-deficient region, resulting in a great drop in corrosion resistance. . Usually long-term use in the later stage will produce the most worrying intergranular corrosion of stainless steel in the weld. If the carbon content of the stainless steel is too high, the stainless steel pipe will be inadvertently caused at the weld, and the defect will definitely be It will appear after a certain period of use, and it cannot be tested on the spot. The third point is the problem of thermal expansion and contraction. The destructive force of stainless steel plate material with temperature changes is very strong, so thermal expansion and contraction is very important for stainless steel materials. The effect of thermal expansion cannot be simply determined by the value of the pulling force when the product is produced. For example, the threaded connection that was originally used is very susceptible to thermal expansion and contraction, because stainless steel pipes and fittings are not extended or shortened. Frequent fatigue bursts often occur, and the greater the temperature difference, the greater the destructive power. Therefore, if the connection between the stainless steel pipe and the pipe fitting is buried, the thermal expansion and contraction performance of the material must be fully considered. However, it is difficult to achieve the consistency of the parent pipe and the pipe fitting and the weld by the argon arc welding. The stress is relieved, especially in the northern pipelines, mostly in the summer and autumn, which leads to the maximum negative temperature difference of about 35 degrees when the water pipe is generated and buried. Especially when the temperature drops rapidly, the pipe is axially affected without the installation of the pipe expansion joint. Pulling will cause the cracking of the pipe and the pipe fitting. Once the treatment is not good, the existing pores, the virtual welding, etc. are defects that are destroyed during the thermal expansion and contraction, and will be exposed over time, so in the case of burying It is important to pay attention to the use of a reasonable installation process. Source: China Stainless Steel Pipes Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

Due to the excellent performance of seamless stainless steel pipes, the use is very popular and the price is very reasonable. Therefore, in the downstream spot market, there are counterfeit and seamless stainless steel pipes, which are fluid pipes. In fact, this pipe is treated high. Frequency welded pipe. The treatment method of the high-frequency welded pipe is to scrape or wear off the original weld by special equipment. Another method is to hot-roll the welded pipe. Some unscrupulous merchants use this kind of pipe to deceive the purchaser. Let’s talk about the characteristics of this pipe. First of all, if it is shaved or worn away, it will leave traces. Some of them are obvious. Sometimes it is more obvious after removing the rust with tools. The manufacturers of such pipes are marked with the quality certificate because they are afraid of taking responsibility. Fluid pipes instead of seamless steel pipes for labeling fluids; merchants selling such pipes usually have to settle according to the theoretical weight, but the real domestic seamless steel pipes are beyond the standard thickness, generally overweight; there is a more professional, That is to do the flaw detection and component inspection, but these two methods are more limited, because the flaw detection is difficult to identify the hot-rolled welded pipe. The seamless stainless steel pipe is heat-shrinked and the appearance is also more beautiful, so that the overall performance of the stainless steel pipe can be increased. Commonly used welded pipes in the market mainly include straight seam welded pipes, spiral welded pipes and seamless welded pipes, but straight seam welded pipes and spiral welded pipes are very well recognized. The difference between seamless welded pipes and seamless pipes is mainly reflected in the following aspects. First, the welded pipe is usually fixed length and is usually 6 meters, 9 meters or 12 meters. There are very few fixed-length steel pipes, because the factory has a lot of price increases. Secondly, from the cross section of the stainless steel pipe head, if there is rust, wipe it clean and look carefully to find the weld zone. And if it is pickled, it will be more obvious. In addition, it should be noted that the general thick-walled steel pipe does not have the phenomenon of welded pipe spitting, and only the thin-walled steel pipe is easy to be confused, but it is also distinguishable. It can be observed whether the wall thickness of the stainless steel pipe is uniform, because the seamless steel pipe is made of round steel perforation, so the wall thickness of the seamless steel pipe usually varies, and the welded pipe is processed by welding or thermal expansion, but because of its The raw material is stainless steel strip, so the wall thickness of the welded pipe is very uniform. Source: China Stainless Steel Pipes Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

1 Overview In recent years, the output of the world’s duplex stainless steel is growing, accounting for about 1% to 2% of the total stainless steel production. The output of China’s duplex stainless steel has grown significantly with the production of stainless steel (annual output of 6.943 million tons in 2008 and steel self-sufficiency rate of 82%). In 2008, the domestic crude steel output of duplex stainless steel was 16,867 tons. , an increase of 1.6 times over 2007. With the commissioning of advanced process equipment, the specifications of China’s duplex stainless steel have also made great progress. For example, Taigang’s equipment has been able to produce 3000mm wide plate, 2000mm wide hot rolled coil and 0.6mm x 1500mm cold rolled coil. Baosteel can produce 4000mm wide plate and 1600mm wide hot rolled coil. For example, Zhejiang wilsonpipeline Pipe Industry Co., Limited. has built a full-automatically controlled steel pipe hot extrusion production line, which provides a possibility for the future production of super and even super duplex stainless steel pipes. There has also been great progress in process technology. Taigang uses AOD furnace to smelt nitrogen-containing stainless steel, and establishes a nitrogen alloying process model, which can accurately control the nitrogen content in the finished product to reach ±0.0135%. In addition, the P and S content in the finished product can be controlled to a lower level. The performance of the series of duplex stainless steel products, especially the performance of high-nitrogen duplex stainless steels is guaranteed. In addition, the production process of duplex stainless steel plate has been mature, the production of hot and cold rolled coils of duplex stainless steel can completely reduce imports, and some large-diameter thick-walled tubes that have been successfully produced by some manufacturers such as Pangang Group have also achieved Breakthrough progress. The advantage of duplex stainless steel is its superior corrosion resistance, especially resistance to localized corrosion. In the case of large fluctuations in nickel prices, the development of nickel-saving economical steel grades has become a key promotion product. On the other hand, in the harsh and corrosive environment, due to its high cost performance, the development of high grade steel grades has also become one of the important development directions. Another advantage of duplex stainless steel is that it has twice the strength and good toughness of austenitic stainless steel, which is the development goal of foreign duplex stainless steel in recent years, that is, not only used in the traditional papermaking and chemical processing industries. The equipment also utilizes its high strength and good fatigue resistance for important utilities such as bridges and road construction. In the following two aspects of materials and applications, the development trend of duplex stainless steel in the development and application of steel in recent years is outlined. 2 Development trend of steel grades Economical duplex stainless steel There are three kinds of new mature steels developed abroad: one developed by Armco Nitronic of the United States and incorporated into the ASTM A240/A240M steel plate standard, under the designation UNSS32001, and the company code is 19D, which is a new steel grade that is not easy to produce δ phase. , has been used in deep sea pipelines and car frames. The other was developed by the Outokumpu company in Finland in 2002. The company name is LDX 2101. In 2006, it was incorporated into the US standard under the designation UNSS32101. It can be used to manufacture process equipment for medium corrosive environments, such as white liquor tanks in paper mills. wide. In recent years, special attention has been paid to the development of steel grades for infrastructure, and it has been successfully used in the construction of bridges and the like. The two steels are all made of Mn and N, which reduce the content of Ni and Cr. Their corrosion resistance and 304LH are cheaper because they do not contain Mo, but they are not suitable for the structure of the sea. The third is AL2003 steel developed by Allegheny Technologies of the United States, which has been incorporated into the US standard under the designation UNSS32003. It has a nickel content of 3.5%, is higher than the former two steels, and contains 1.7% Mo, which can be used for depths up to 1200m. The high-pressure pipeline system that transports sulfur-free or mild sulfur-containing oil and gas on the seabed. Combined with the domestic resources, it is considered that this type of steel has development value. It is necessary to have a more promising economical dual-phase steel in a medium corrosive environment. Currently, development of LDX2101 steel is underway, and composition optimization and welding are required. In-depth study of process and performance. super duplex stainless steel The SAF2507 steel developed in Sweden is a widely used steel grade in super duplex stainless steel. It has been incorporated into many national standards. It has a good phase balance and is easier to master the production process in the same kind of steel, especially in the case of high chloride. It has excellent local corrosion resistance and is commonly used in seawater heat exchangers, pipeline cables in seabed oil fields, seawater desalination, flue gas desulfurization and other devices. The UK has developed Zeron 100 steel with W and Cu, which has been successfully used in seawater jet pumps, lift pumps, etc. due to its good wear and corrosion resistance. From a technical point of view: the offshore industry is a more meaningful place to use super duplex stainless steel, but in order to adapt to the current improved oil and gas recovery method, the wellhead control system requires higher corrosion resistance and the deep sea submarine temporary pipeline and pipeline cable. Demand, existing steel grades have been insufficient in strength and corrosion resistance, Sweden Sandvik company has designed a series of super super duplex stainless steel SAF2906, SAF2707HD, SAF3207HD and other high strength and excellent corrosion resistance up to 1000MPa Steel type. At the same time, the United States Langley Alloys developed a sulfur content of 0.001%, the addition of copper Ferralium 225-SD50 steel, not only improved its resistance to pitting and crevice corrosion in seawater, its strength is also higher than other super duplex stainless steel 10 %. In addition, recently developed for special applications, there are 29% Cr, 0.4% N SAFUREX new steel grades for Stamicarbon urea stripper, which can replace 2RE69 austenitic steel. In order to handle the chloride food tank, Japan has also developed NARDP-3W steel with 2% W, as well as DP28WTM steel with better corrosion resistance, mechanical properties, formability and weldability. 3 Promotion and expansion of applications Duplex stainless steels are used in a wider range of applications, and have traditionally utilized their superior resistance to localized corrosion, especially stress corrosion resistance, as a corrosion resistant functional material. In recent years, from the perspective of its strength, the application of duplex stainless steel as a modern structural material deserves attention. Chemical tanker The wave wall cargo tank of a chemical tanker is also one of the typical strengths of duplex stainless steel. In the 1970s, France used the UR 5O (00Cr21Ni7Mo3Cu) steel without nitrogen to make the cabin. Today, Industeel and Arcelor Group received more than 70% of the UR 45N (2205) steel. Based on an in-depth study of the compatibility of stainless steel materials with cargo and the technical support of steel companies, UR 35N (2304) will also have a good development prospect. In 2002, Hubei Qingshan Shipyard used the UNSS3I803 (2205) wave wall board produced by Arcelor to build a 18,500-ton chemical tank cargo tank for the Belgian shipowner, and several other ships were built one after another. Recently, Yangzi Shipyard signed a contract for the supply of 2205 duplex stainless steel by Outokumpu to manufacture four 3600-ton chemical tankers. In 2007, TISCO first supplied the domestic 2205 duplex stainless steel to the Chuandong Shipyard to produce 9000 tons of cargo tanks (using 2,205 and 600 tons), 5,500 tons and 3,750 tons of cargo tanks. Contracts are still being signed for supply. 22-09 welding rods are also supplied domestically, but the welding wire still needs to be imported. This is a big breakthrough. China Classification Society has also incorporated 2205 (S32205), 2507 (S32750) and copper-containing 2506 (S32550) three steel grades into the human-level specification. Building structure •Bridge and concrete reinforcement In recent years, there have been more than ten bridges in the world using duplex stainless steel, mostly pedestrian bridges. For example, the earlier York Bridge in England and the Aparte Bridge in Sweden used 2205 steel. In recent years, the new bridge in Norway and the Rffolo bridge in Italy have used the economical 2101 steel. Nearer duplex stainless steels have also begun to be used in highway bridges, especially those that are sensitive to chloride induced corrosion. New York’s Brooklyn Bridge uses 2205 steel bars. The steel’s high strength and high elongation give it excellent fatigue resistance and life is more than 2 times higher than ordinary steel. The Stonecutters Bridge in Hong Kong, China, uses about 2,000 tons of 2205 steel plates to make the outer surface structure of the upper part of the pylon. The estimated life is 120 years from maintenance. From the Hong Kong to Shenzhen 3.2km long expressway bridge across the bay, about 1,250 tons of 2205 and 316 are used as high-speed road reinforcement. In addition, Wuhan Tianxingzhou Bridge is a cable-stayed bridge for both public and railway use. It uses 20 tons of 2205 10~20mm plates produced by Taigang, cut short and welded into angle steel, which is used as a component for connecting piers and diagonally-reinforced steel bars. •Building facilities Barcelona, Spain used 500 tons of 4mm thick 2101 to build a flour storage bin. In the United States, 1,500 tons of AL 2003 sheets processed by matt surface were used to build the world’s larger stainless steel roof (the roof of Qatar Doha International Airport). India provided 200 tons of surface electropolished 2101 duplex stainless steel sheets from Outokumpu. 2025mm, Ф38mm, Ф50mm three kinds of 20km long welded pipe, will be used for the handrail of the Mumbai street overpass. Deep sea oil field As the demand for oil and gas grows, driving operators to mine deeper and farther subsea oil fields has rapidly increased the use of deep-sea oil wells. The main production platform implements a standardized pipeline harness operation to provide water, power, decompression, and uphole communications from the well bore. In addition, in order to ensure the fluidity of the oil, injection of chemical agents is required in many deep-sea return pipes, and in order to increase production, oil well acidification is also carried out through pipeline cables. Pipeline cables have become the lifeblood of subsea mining systems. Facing the deep sea exposure environment means that the pipeline cable needs to be highly mechanical, resistant to internal and external corrosion, and resistant to stress corrosion cracking. The preferred material for deep-sea pipelines should be super and ultra-super duplex stainless steel, but due to price and manufacturing problems, galvanized 19D duplex stainless steel (ZCLDSS) has been developed, and the design life of the pipeline cable is 20 years. Has been promoted and applied. In addition, the economical low-nickel AL 2003 steel has also been used in 2006 for submarine pipelines with a depth of more than 1200 m in the East Malaysia oil field. The copper-added Ferrallium 225-SD50 duplex stainless steel has become the container material for 7000m deep seabed equipment and cables, and has been developed as a highly accurate subsea locator and controllable deep sea acoustic transponder pressure housing and load bearing components (7000m sea) Deep is about 700 atmospheres, HI 2.5 tons load). Sweden’s Sandvik’s newly developed SAF 2906 and SAF3207 super duplex stainless steels are ultra-high strength and corrosion resistant, with high operating temperatures of 60 and 90 ° C, respectively. Other industries •Seawater desalination At present, the desalination industry is growing rapidly. Half of the plants are now in the Middle East. The more common methods of desalination have multi-stage flash (MSF) and reverse osmosis (RO). In recent years, advances in thin film technology have led to an increase in the use of RO. trend. The condenser tube of the MSF evaporator should use 2507 super duplex stainless steel tube instead of titanium or copper-nickel alloy. The flash chamber housing can be used 2205, which has been adopted in Libya. The high pressure pipe of the RO method and the high pressure pump of the high chloride environment are made of 2507 steel, which is comparable to the austenitic steel with 6% Mo and has been used in the newly built Ashkelon plant in Israel. The project on Caofeidian in China is to use a 300-ton 2205 steel plate supplied by Outokumpu to make a multi-stage flashing device of 1OOm×25m×6m. Usually 1.2 million tons of processing equipment requires 10,000 tons of 6mm thick steel plates. China’s fresh water resources are insufficient, the coastline is long, and desalination will be put on the agenda, which will be the potential use of duplex stainless steel. •Fume desulfurization (FGD) The FGD system is used to eliminate SO2 from flue gas from coal-fired power plants, reduce emissions to the atmosphere, and prevent acid rain. Forecasts indicate that two-thirds of the world’s coal-fired power plants will be equipped with FGD units by 2020. At present, the wet FGD device is dominant, mainly using limestone mud to neutralize and clean the exhaust gas in the absorption tower. At the population of the device, the high-temperature exhaust gas forms a high concentration of high-temperature sulfuric acid, and a high-molybdenum nickel-based corrosion-resistant alloy is required. However, after reacting with the lime mud, the pH is raised and the temperature is lowered. At 55 ° C, pH > 6, Cl – concentration below 30,000 ppm can choose 2205 steel, better than 317LMN effect. Super-phase duplex stainless steel can also be used if the Cl- concentration is higher and the pH is lower. The Coleson Cove Power Plant in Canada is based in the United States on the top of the absorption tower with 360 tons of 2205 duplex stainless steel. Most of China is a coal-fired power plant, and a large number of FGD systems will open up a new market for duplex stainless steel. The 1.4475 wear-resistant and corrosion-resistant duplex stainless steel GX150CrNiMoCuN41-6-2 developed in Germany is composed of a network of high-chromium carbides with a volume of 25% to 30%, which improves the wear and corrosion resistance. The impeller used in the Niederau β em power plant for the manufacture of FGD recirculating filter pumps works well with solid particles up to 25%, pH > 4 and chloride content 5.5%. The above is the progress in the application of foreign countries in recent years. Some domestic ones have just begun, and some have not yet been put on the agenda. For many years, Taigang has provided 2205 composite plates for the Three Gorges and Wanxian, Lantian and other plants in water conservancy projects and salt production. Fortunately, TISCO has been able to provide super duplex stainless steel 2507 composite plates for coking projects. Zhenhai Refinery uses 2205 welded pipe instead of heat exchanger made of seamless pipe. The welded pipe made of 1m×6.5mm plate is used as the conveying pipe in Guangxi Million Ton Refinery. This is a new breakthrough in the refinery. Development prospects. At present, the manufacture and use of plate heat exchangers have been put on the agenda, which puts new demands on domestic cold rolled coils. In recent years, Baosteel Wugang Co., Ltd. and Special Stainless Steel Co., Ltd. and Jiuli Group Co., Ltd. have also provided seamless steel pipe replacement for the West-East Gas Pipeline Project. Pangang Group Chengdu Iron and Steel Co., Ltd. successfully produced 295mm × 45mm large diameter thick Wall pipe, Wujin Stainless Steel Pipe Factory has already mass-produced Ф108～25mm×3～10mm steel pipes of 2205 and 2506 steel. In addition, in terms of exports, China’s pulp evaporating tanks manufactured by Indonesian paper mills, the 800 tons of 2,304 plates and the renewed 2000 tons of plates required for the first phase of the outsourcing project are all supplied by Taigang and supplied to the Dutch ship propellers. The board also has hundreds of tons of 2304 steel plates. The potential use of duplex stainless steel is very wide and it remains to be developed in China. 4 Suggestions for developing duplex stainless steel in China To promote the development of duplex stainless steel in China, the following are recommended: Use a variety of propaganda methods to increase publicity. Key development requires large quantities, widely used, and more mature craftsmanship, such as 2205, 2304 and other conventional steel grades. Actively promote the production and application of economical duplex stainless steel such as 2101. Further research and development of special super duplex stainless steel to meet the needs of higher corrosion resistance, higher strength and higher temperature. In terms of use, in addition to continuing to develop in the fields of water industry, petrochemical, salt production, chemical tankers, etc., it is necessary to expand heat exchangers, containers, and storage in oil and gas, environmental protection, seawater desalination, marine engineering, building structures and manufacturing. The development of industrial uses such as tanks and the development of potentially huge civilian markets. The current domestic main products are medium and heavy plates produced by single-roll mills. In order to improve efficiency, hot-rolled coils (shear plates) are produced by continuous rolling and hob rolling mills. The key to expanding the application is to speed up the trial production and supply of thin gauge cold rolled duplex stainless steel coils. It is also necessary to accelerate the production and development of pipes, long products, and supporting products such as castings, forgings and welding consumables. Master the welding process characteristics and welding materials of duplex stainless steel and austenite. Organize the joint research of upstream and downstream enterprises and production and research institutes of production enterprises and units, strengthen the exchange of technology at home and abroad, and promote the development of duplex stainless steel. Source: China Stainless Steel Fittings Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

The stainless steel pipe in the passivated state still has a certain reaction ability because its passivation film is always in a state of dynamic equilibrium of dissolution and repair and repassivation. When the stainless steel pipe is in an environmental medium containing active anions, the equilibrium state is easily destroyed, and the dissolved state at this time is more dominant. The reason for this is that a living anion such as chloride ion preferentially adsorbs on the passivation film on the surface of the stainless steel pipe, and discharges the original oxygen atom, and then combines with the cation in the passivation film to form a soluble chloride. The result is that small etch pits are formed at specific points of the newly exposed base metal. The pore size of such small etch pits is mainly around 20-30 μm. These small etch pits are called pitting cores. Understand the active center formed by the etched holes. The presence of chloride ions acts as a direct destructive effect on the passive state of the stainless steel pipe surface. Generally, the range of the passivation zone on the surface of the stainless steel pipe decreases as the chloride ion concentration increases. In practical applications, when the anode potential in the environmental medium reaches a certain value, the current density will suddenly become smaller, which indicates that the surface of the stainless steel pipe has begun to form a stable passivation film, and the corresponding resistance will be relatively high, and at a certain potential Long-term maintenance in the region. However, as the concentration of chloride ions in the environmental medium increases, the critical current density increases, the primary passivation potential also increases, and the range of the passivation region is reduced. The explanation for this characteristic is that in the passivation potential region, chloride ions compete with the oxidizing species and enter the film, thereby forming lattice defects and reducing the resistivity of the oxide. Therefore, in an environmental medium in which chloride ions are present, it is neither easy to form passivation nor easy to maintain passivation. When the local passivation film of the stainless steel pipe is damaged, the remaining protective film remains intact, which enables the pitting conditions to be achieved and strengthened. According to the electrochemical formation mechanism, the stainless steel in the activated state has a much higher electrode potential than the passivated stainless steel, and the electrolyte solution reaches the thermodynamic condition of electrochemical corrosion, the activated stainless steel becomes the anode, and the passivated stainless steel acts as the cathode. The corrosion point involves only a small portion of the metal, and the other surface will be a large cathode area. In the electrochemical reaction, the cathode reaction and the anode reaction are carried out at the same speed, so the corrosion rate concentrated on the corrosion point of the anode is fast, and the penetration effect is remarkable, so that pitting corrosion is generated. Source: China Stainless Steel Pipes Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

Stainless steel corrugated metal hose (referred to as metal hose) is a flexible connecting pipe widely used in modern industrial pipelines. It consists mainly of a flexible body (corrugated pipe), a mesh body and various types of joints. Its inner tube is a thin-walled stainless steel corrugated tube with a spiral shape or a ring shape. The outer sleeve of the bellows is woven by stainless steel wire, steel wire braid or steel strip according to certain parameters. The joints at the ends of the metal hose can be fitted according to the user’s pipe or the joint of the equipment. Construction of stainless steel corrugated metal hose: The bellows part is a thin-walled seamless or longitudinal welded stainless steel thin-walled tube that has been shaped by high-precision plastic shaping. The elastic characteristics of the bellows profile determine the softness and fatigue resistance of the hose, and it is easy to absorb various motion deformations and cyclic loads, especially to compensate for the large displacement of the system. Since the main parts of the hose are made of austenitic stainless steel, the hose has excellent temperature resistance and corrosion resistance. The hose has a wide operating temperature range of -196-600 °C. Corrosion resistance of the hose can be ensured by selecting the applicable stainless steel grade according to the corrosiveness of the medium through the pipeline. The metal hose is made of 1Cr18Ni9Ti stainless steel as a whole and has strong corrosion resistance. The hose body is hydroformed by a thin-walled stainless steel pipe body, which has strong flexibility, flexibility, bending and vibration resistance, and enhanced protection of the woven mesh sleeve to make it have higher pressure bearing capacity. The connection at both ends of the hose can also be made in other ways than the thread and flange standards for easy connection and use. This product is not only suitable for use with rotary joints, but also widely used for flexible connections in a variety of fluid media delivery. Stainless steel corrugated metal hose features: It has good softness, fatigue resistance, high temperature resistance and corrosion resistance. It has a much higher life than other types of hoses (rubber and plastic hoses). With the development of modern industry, it has high temperature resistance and high pressure resistance. Corrosion-resistant stainless steel metal hoses will become more and more widely used. Source: China Metal Hoses Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

Because of the many types of stainless steel pipes, many of the standard brands are listed, and there are many non standard grades which are widely used in fashion. These brands have different performance and are widely used in fashion. These brands have different performance, so it is very difficult to choose the suitable grades of stainless steel pipes. It involves expertise in many disciplines such as materials science, corrosion science and engineering. Before selecting stainless steel pipes, the use of stainless steel pipes and the use environment should be considered. For example: decoration used in general use of welded pipe, fluid transport generally seamless pipe, medical or kitchen to use sanitary stainless steel pipe, pressure use thick wall pipe; general indoor use of 200 series of materials, outdoor use of 304 and other materials, and in the acid and alkali local or coastal areas generally use more than 316 material. When selecting steel pipes, it is necessary to make sure that the material is up to the standard. Take 304 material as an example:                                                                                                                                                                    1). from the price analysis, if the 304 material stainless steel pipe is even lower than the general price of the 301 material on the market, it is very likely that other materials are impersonating. 2). recognize whether the “304” mark on the pipe surface is required, and obtain the manufacturer’s quality certificate as the voucher. 3). can be tested with acid reagent. After 304 seconds, 304 will not change color and 201 will turn black. 4). large quantities of purchased samples can be sent to the national authoritative Inspection Center for component analysis. To see whether the color of the outer surface and the inner wall of the pipe is bright and smooth, whether the thickness is uniform or rough. The general welded pipe does not need to be checked, but the seamless steel pipe is produced by cold drawing or hot rolling. In the process of production, it is easy to produce uneven thickness and cracks in the pipe surface, and the surface roughness is generally seamless pipe without polishing treatment. If there is no special requirement on appearance, it does not affect the use. When purchasing, we should select excellent products evaluated by the quality and Technical Supervision Bureau. Long term use of testimony and good reputation is the most direct and effective way to purchase customers. Internal heavy skin, pitting, and rolling green line are often found in the rolling pipe. In general, these can not be avoided, but it does not affect the use, but we must choose as few as possible when choosing, especially the inner surface. Source: China Stainless Steel Pipes Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

The stainless steel water pipe does not mean that it will not rust, but it is not easy to rust with respect to iron and copper pipes. A good quality stainless steel water pipe for a dozen years is still not a big problem, but it should be used well. The stainless steel water pipe is not easy to rust, because the stainless steel pipe is nickel-chromium alloy steel. After the nickel-chromium content reaches a certain condition, a protective film is formed on the surface of the steel pipe to protect the steel pipe from rust. However, once the external force or corrosive environment destroys the protective film, the steel pipe is easily rusted. The six types of rust that are common in stainless steel water pipes and their treatment are as follows: 1. Rusted by dissimilar metals Here, it refers to a dissimilar metal such as iron that is easily rusted. It is caused by iron powder iron cutting. If the situation is not serious, it can be wiped directly with sponge or cloth with neutral detergent or soapy water. However, if the situation is serious and brown rust has been formed, it will be used on the market. A special cleaning agent or a 15% sulfuric acid dilution is used for cleaning. 2. Attachment to rust caused by harmful components in the exhaust Under the influence of harmful components contained in automobile exhaust, air-conditioning, or factory exhaust, stainless steel pipes are prone to rust spots. The processing can be handled in the first case. However, if in this environment, it is necessary to do 2-3 times of comprehensive cleaning work every year. 3. Rusting due to salt adhesion In the coastal area, the front side is blown by the sea breeze, and the 304 stainless steel pipe will also generate red rust in a short period of time. Moreover, it rusts faster than other areas, and the treatment method is the same as the first case. In the coastal area, when using stainless steel exteriors, it is desirable to use stainless steel pipes of 316 material with higher corrosion resistance. 4. Rusting caused by attached cleaning solution If it cannot be removed with a neutral detergent, use a cleaning solution to remove it. 5. Rusting due to fingerprints or hand scales If it cannot be removed with a neutral detergent, use a sponge, cloth, etc., with an organic solvent (alcohol, acetone, light oil, etc.) to wipe. If this method is still not completely removed, use stainless steel with a cleaning solution to remove it. In short, after cleaning various cleaning methods, it is necessary to use clean water for final cleaning. 6. Contamination caused by surface protective film Wipe with a sponge, cloth dampened with a water-soluble neutral detergent, or alcohol. If it is still invalid, use a thinner and light oil to remove it. Rinse thoroughly with clean water after washing. Source: China Stainless Steel Water Pipes Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)